One more comment...
From my perspective, getting the kit lens would be a no brainer. From what I can see of prices at UK Stores like Jessops, it's adding very little to the cost of a 450D kit. For example, they're getting £459.99 for a 450D body only there, and you can buy a 450D with an 18-55mm IS lens for only £499.99 there. That lens sells for £159.99 separately at Jessops. So, the kit with it included is a bargain. If you decide you don't like the lens, sell it. ;-) You're not paying much for it compared to it's value, and I think it's probably unlikely you'd lose money if you sold it, since you're paying so little for it in a kit.
Even if you did, consider it a tuition fee. By using a lens like that for a while, you'll have a better understanding of what you may or may not need later for the type of shooting you do more often.
P.S. -- I'd probably compare prices on the two lens kit also (including both the 18-55mm and 55-250mm IS lenses) to see how much of a bargain it is compared to buying the lenses separately (I haven't researched it). That way, you'd have roughly the same coverage you have with your FZ30 (that two lens kit would give you the same range (same angle of view) you'd have using lenses that cover 29-400mm with a 35mm camera).